1. Technical Field
The present invention generally relates to high water content silicone hydrogel materials.
2. Description of the Related Art
Hydrogels represent a desirable class of materials for contact lenses. A hydrogel is a hydrated cross-linked polymeric system that contains water in an equilibrium state. Hydrogel lenses offer relatively high oxygen permeability as well as desirable biocompatibility and comfort.
Oxygen permeability (Dk) is one important factor in contact lens design to maintain ocular health for contact lens wearers. For example, a contact lens must allow oxygen to reach the cornea in an amount which is sufficient for long-term corneal health. The contact lens must also allow oxygen from the surrounding air to reach the cornea because the cornea does not receive oxygen from the blood supply like other tissue. “Soft” contact lenses conform closely to the shape of the eye, so oxygen cannot easily circumvent the lens. Thus, soft contact lenses must allow oxygen to diffuse through the lens to reach the cornea.
Another ophthalmic compatibility requirement for soft contact lenses is that the lens must not strongly adhere to the eye. Clearly, the consumer must be able to easily remove the lens from the eye for disinfecting, cleaning, or disposal. However, the lens must also be able to move on the eye in order to encourage tear flow between the lens and the eye. Tear flow between the lens and eye allows for debris, such as foreign particulates or dead epithelial cells, to be swept from beneath the lens and, ultimately, out of the tear fluid. Thus, a contact lens must not adhere to the eye so strongly that adequate movement of the lens on the eye is inhibited.
In order to balance the ophthalmic compatibility and consumer comfort requirements in designing a daily wear soft contact lens, high water content conventional hydrogel contact lenses composed of copolymers of hydrophilic monomers such as 2-hydroxyethyl methacrylate) (HEMA), N-vinylpyrrolidone and the like, and prepared by lathe-cutting methods, spin casting methods, cast molding methods or combinations thereof, followed by a swelling treatment in a physiological saline and/or phosphate buffer solution to obtain lenses with water contents of about 20% to about 80% by weight were developed. These hydrophilic polymers move well on the eye and provide sufficient oxygen permeability for daily wear.
Prior art soft silicon-containing hydrophilic contact lenses with higher water contents tend to have reduced or lower oxygen permeabilities. For example, a silicone hydrogel contact lens available under the tradename, Focus Night & Day (available from CIBA Vision Corporation), has a water content of about 24% and a Dk of about 140 Barrers. Another silicone hydrogel contact lens available under the tradename, O2 Optix (available from CIBA Vision Corporation), has a water content of about 33% and a Dk of about 110 Barrers. Another silicone hydrogel contact lens available under the tradename, Acuvue Oasys (available from Johnson & Johnson), has a water content of about 38% and a Dk of about 105 Barrers. Another silicone hydrogel contact lens available under the tradename, PureVision (available from Bausch & Lomb), has a water content of about 36% and a Dk of about 100 Barrers. Another silicone hydrogel contact lens available under the tradename, Acuvue Advance (available from Johnson & Johnson), has a water content of about 46 to 47% and a Dk of about 65 Barrers. In comparison, a non-silicone hydrogel contact lens available under the tradename, Acuvue2 (available from Johnson & Johnson), has a water content of about 58% and a Dk of about 25 Barrers.
U.S. Pat. No. 5,260,000 discloses a process for preparing silicone hydrogel contact lenses, where silicone hydrogel contact lenses are cast from monomeric mixtures including a major amount of a silicone-containing monomer, a hydrophilic monomer and n-nonanol or n-hexanol as a diluent, and subsequently extracted with isopropanol to remove any remaining diluent as well as unreacted monomers and oligomers. However, problems associated with the manufacturing of low cost lenses from silicone hydrogels include the need for a solvent extraction step in the manufacturing process to remove any unreacted silicone as well as the need to perform a post-polymerization surface modification step(s) to provide a wettable, lubricious and low-fouling surface.
U.S. Pat. No. 7,268,198 (“the '198 patent”) discloses a silicone hydrogel that is the hydrated polymerization product of a monomer mixture comprising a hydrophilic monomer selected from the group consisting of N-vinyl-N-methyl acetamide, N-vinyl-N-ethyl acetamide, N-vinyl-N-ethyl formamide, N-vinyl formamide, N-vinyl pyrrolidone and mixtures thereof, and a polysiloxane-containing monomer, wherein the hydrogel has an oxygen permeability of at least about 120 Barrers and a modulus from 40 to 57 g/mm2. However, each of the examples in the '198 patent form a silicone hydrogel having a water content between 19.2% and 35.3%.
It would be desirable to provide improved high water content silicone hydrogels.